Increased expansion ratio, cell density, and compression strength of microcellular poly(lactic acid) foams via lignin graft poly(lactic acid) as a biobased nucleating agent

Green and renewable foaming poly(lactic acid) (PLA) represents one of the promising developments in PLA materials. This study is the first to use the lignin graft PLA copolymer (LG-g-PLA) to improve the foamability of PLA as a biobased nucleating agent. This agent was synthesized via ring-opening polymerization of lignin and lactide. The effects of LG-g-PLA on cell nucleation induced by the crystallization, rheological behavior, and foamability of PLA were evaluated. Results indicated that LG-g-PLA can improve the crystallization rate and crystallinity of PLA, and play a significant nucleation role in the microcellular foam processing of PLA. LG-g-PLA improved the foam morphology of PLA, obtaining a reduced and uniform cell size as well as increased expansion ratio and cell density. With the addition of 3 wt% LG-g-PLA content, the PLA/LG-g-PLA foams increased the compressive strength 1.6 times than that of neat PLA foams. The improved foaming properties of PLA via a biobased nucleating agent show potential for the production and application of green biodegradable foams.